Sorry Rao, I know you prefer an all-or-nothing approach, and I can see why. But I also voted "some." I'd stick with just the annuals.
I also wonder if we even want to get into the whole Earth-1 and Earth-2 thing. As Nightwing pointed out, Fleisher approached the work as if it was all one Superman, one Luthor, etc. remaining ageless through the years. Splitting characters into multiple versions would be a big mess.
Perhaps we could handle it the way Fleisher does, and just say something like, "...where Luthor encounters a version of himself from a parallel dimension" or "an alternate dimension" or something like that. I'm pretty sure I've already seen him do this somewhere.
Ditto what Starchild said. I suggest we approach it like Fleisher approached his non-canonical sources (like the newspaper strip, Batman comics, etc).
Can anyone name 5 first appearances or major stories from DCCP?